Method for receiving downlink data channels in multicell-based wireless communication systems and apparatus for same

ABSTRACT

The present invention relates to a method by which a terminal receives a downlink data channel based on a terminal-specific reference signal in a wireless communication system. In detail, the method includes the steps of: receiving from a network information on one or more settings defining large scale properties of a terminal-specific reference signal through a higher layer; detecting from the network scheduling information on a downlink data channel based on a terminal-specific reference signal; and receiving from the network the downlink data channel based on the terminal-specific reference signal on the basis of the scheduling information, wherein the scheduling information includes an indicator indicating one or more of the settings.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2013/001071, filed on Feb. 12, 2013, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application No. 61/597,725filed on Feb. 11, 2012 and 61/669,655 filed on Jul. 9, 2012, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of receiving a downlink data channel in amulticell-based wireless communication system and an apparatus therefor.

BACKGROUND ART

3GPP LTE (3^(rd) generation partnership project long term evolutionhereinafter abbreviated LTE) communication system is schematicallyexplained as an example of a wireless communication system to which thepresent invention is applicable.

FIG. 1 is a schematic diagram of E-UMTS network structure as one exampleof a wireless communication system. E-UMTS (evolved universal mobiletelecommunications system) is a system evolved from a conventional UMTS(universal mobile telecommunications system). Currently, basicstandardization works for the E-UMTS are in progress by 3GPP. E-UMTS iscalled LTE system in general. Detailed contents for the technicalspecifications of UMTS and E-UMTS refers to release 7 and release 8 of“3^(rd) generation partnership project; technical specification groupradio access network”, respectively.

Referring to FIG. 1, E-UMTS includes a user equipment (UE), an eNode B(eNB), and an access gateway (hereinafter abbreviated AG) connected toan external network in a manner of being situated at the end of anetwork (E-UTRAN). The eNode B may be able to simultaneously transmitmulti data streams for a broadcast service, a multicast service and/or aunicast service.

One eNode B contains at least one cell. The cell provides a downlinktransmission service or an uplink transmission service to a plurality ofuser equipments by being set to one of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz,15 MHz, and 20 MHz of bandwidths. Different cells can be configured toprovide corresponding bandwidths, respectively. An eNode B controls datatransmissions/receptions to/from a plurality of the user equipments. Fora downlink (hereinafter abbreviated DL) data, the eNode B informs acorresponding user equipment of time/frequency region on which data istransmitted, coding, data size, HARQ (hybrid automatic repeat andrequest) related information and the like by transmitting DL schedulinginformation. And, for an uplink (hereinafter abbreviated UL) data, theeNode B informs a corresponding user equipment of time/frequency regionusable by the corresponding user equipment, coding, data size,HARQ-related information and the like by transmitting UL schedulinginformation to the corresponding user equipment. Interfaces foruser-traffic transmission or control traffic transmission may be usedbetween eNode Bs. A core network (CN) consists of an AG (access gateway)and a network node for user registration of a user equipment and thelike. The AG manages a mobility of the user equipment by a unit of TA(tracking area) consisting of a plurality of cells.

Wireless communication technologies have been developed up to LTE basedon WCDMA. Yet, the ongoing demands and expectations of users and serviceproviders are consistently increasing. Moreover, since different kindsof radio access technologies are continuously developed, a newtechnological evolution is required to have a future competitiveness.Cost reduction per bit, service availability increase, flexiblefrequency band use, simple structure/open interface and reasonable powerconsumption of user equipment and the like are required for the futurecompetitiveness.

DISCLOSURE OF THE INVENTION Technical Task

Accordingly, the present invention intends to propose a method receivinga downlink data channel in a multicell-based wireless communicationsystem and an apparatus therefor in the following description based onthe discussion mentioned earlier in the foregoing description.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of receiving a UE-specific reference signalbased-downlink data channel, which is received by a user equipment in awireless communication system, includes the steps of receivinginformation on one or more configurations defining large scale propertyof the UE-specific reference signal from a network via an upper layer,detecting scheduling information of the UE-specific reference signalbased-downlink data channel from the network and receiving theUE-specific reference signal based-downlink data channel from thenetwork based on the scheduling information, wherein the schedulinginformation includes an indicator indicating one of the one or moreconfigurations.

Meanwhile, to further achieve these and other advantages and inaccordance with the purpose of the present invention, as embodied andbroadly described, according to a different embodiment, a method oftransmitting a UE-specific reference signal based-downlink data channel,which is transmitted by a network in a wireless communication system,includes the steps of transmitting information on one or moreconfigurations defining large scale property of the UE-specificreference signal to a user equipment via an upper layer, transmittingscheduling information of the UE-specific reference signalbased-downlink data channel to the user equipment and transmitting theUE-specific reference signal based-downlink data channel to the userequipment, wherein the scheduling information includes an indicatorindicating one of the one or more configurations.

Preferably, the information on the one or more configurations caninclude information on a certain reference signal capable of assumingthat the UE-specific reference signal is identical to the large scaleproperty. Moreover, the information on the one or more configurationscan include information on there is no specific reference signal capableof assuming that the UE-specific reference signal is identical to thelarge scale property. In this case, the certain reference signalcorresponds to a channel status information-reference signal (CSI-RS).

More specifically, the information on the certain reference signalindicates resource configuration information of the certain referencesignal.

More preferably, the large scale property corresponds to information ona frequency offset and information on a timing offset forsynchronization tracking. More specifically, the large scale propertyincludes at least one selected from the group consisting of Dopplerspread, Doppler shift, average delay and delay spread.

Advantageous Effects

According to embodiment of the present invention, a user equipment canefficiently receive a downlink data channel in a multicell-basedwireless communication system.

Effects obtainable from the present invention may be non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of E-UMTS network structure as one exampleof a wireless communication system;

FIG. 2 is a diagram for structures of control and user planes of radiointerface protocol between a 3GPP radio access network standard-baseduser equipment and E-UTRAN;

FIG. 3 is a diagram for explaining physical channels used for 3GPPsystem and a general signal transmission method using the physicalchannels;

FIG. 4 is a diagram for a structure of a radio frame in LTE system;

FIG. 5 is a diagram for a structure of a downlink radio frame in LTEsystem;

FIG. 6 is a diagram for a structure of an uplink radio frame in LTEsystem;

FIG. 7 is a diagram for a configuration of a multiple antennacommunication system;

FIG. 8 and FIG. 9 are diagrams of a structure of a reference signal inLTE system supportive of downlink transmission using 4 antennas;

FIG. 10 is a diagram for an example of assigning a downlink DM-RSdefined by a current 3GPP standard document;

FIG. 11 is a diagram for an example of a CSI-RS configuration #0 in caseof a normal CP among downlink CSI-RS configurations defined by a current3GPP standard document;

FIG. 12 is a diagram for an example of a multi node system in a nextgeneration communication system;

FIG. 13 is a diagram for an example of E-PDCCH and PDSCH scheduled bythe E-PDCCH;

FIG. 14 is a diagram of an example for a user equipment to perform atracking to obtain synchronization in a multicell-based wirelesscommunication system;

FIG. 15 is a diagram of an example for a user equipment to perform areference signal tracking according to embodiment of the presentinvention;

FIG. 16 is a diagram of a different example for a user equipment toperform a reference signal tracking according to embodiment of thepresent invention;

FIG. 17 is a block diagram for an example of a communication deviceaccording to one embodiment of the present invention.

BEST MODE Mode for Invention

In the following description, compositions of the present invention,effects and other characteristics of the present invention can be easilyunderstood by the embodiments of the present invention explained withreference to the accompanying drawings. Embodiments explained in thefollowing description are examples of the technological features of thepresent invention applied to 3GPP system.

In this specification, the embodiments of the present invention areexplained using an LTE system and an LTE-A system, which is exemplaryonly. The embodiments of the present invention are applicable to variouscommunication systems corresponding to the above mentioned definition.In particular, although the embodiments of the present invention aredescribed in the present specification on the basis of FDD, this isexemplary only. The embodiments of the present invention may be easilymodified and applied to H-FDD or TDD.

And, in the present specification, a base station can be named by such acomprehensive terminology as an RRH (remote radio head), an eNB, a TP(transmission point), an RP (reception point), a relay and the like.

FIG. 2 is a diagram for structures of control and user planes of radiointerface protocol between a 3GPP radio access network standard-baseduser equipment and E-UTRAN. The control plane means a path on whichcontrol messages used by a user equipment (UE) and a network to manage acall are transmitted. The user plane means a path on which such a datagenerated in an application layer as audio data, internet packet data,and the like are transmitted.

A physical layer, which is a 1^(st) layer, provides higher layers withan information transfer service using a physical channel. The physicallayer is connected to a medium access control layer situated above via atransport channel (trans antenna port channel). Data moves between themedium access control layer and the physical layer on the transportchannel. Data moves between a physical layer of a transmitting side anda physical layer of a receiving side on the physical channel. Thephysical channel utilizes time and frequency as radio resources.Specifically, the physical layer is modulated by OFDMA (orthogonalfrequency division multiple access) scheme in DL and the physical layeris modulated by SC-FDMA (single carrier frequency division multipleaccess) scheme in UL.

Medium access control (hereinafter abbreviated MAC) layer of a 2^(nd)layer provides a service to a radio link control (hereinafterabbreviated RLC) layer, which is a higher layer, on a logical channel.The RLC layer of the 2^(nd) layer supports a reliable data transmission.The function of the RLC layer may be implemented by a function blockwithin the MAC. PDCP (packet data convergence protocol) layer of the2^(nd) layer performs a header compression function to reduceunnecessary control information, thereby efficiently transmitting suchIP packets as IPv4 packets and IPv6 packets in a narrow band of a radiointerface.

Radio resource control (hereinafter abbreviated RRC) layer situated inthe lowest location of a 3^(rd) layer is defined on a control planeonly. The RRC layer is responsible for control of logical channels,transport channels and physical channels in association with aconfiguration, a re-configuration and a release of radio bearers(hereinafter abbreviated RBs). The RB indicates a service provided bythe 2^(nd) layer for a data delivery between the user equipment and thenetwork. To this end, the RRC layer of the user equipment and the RRClayer of the network exchange a RRC message with each other. In casethat there is an RRC connection (RRC connected) between the userequipment and the RRC layer of the network, the user equipment lies inthe state of RRC connected (connected mode). Otherwise, the userequipment lies in the state of RRC idle (idle mode). A non-accessstratum (NAS) layer situated at the top of the RRC layer performs such afunction as a session management, a mobility management and the like.

A single cell consisting of an eNode B (eNB) is set to one of 1.25 MHz,2.5 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz of bandwidths and thenprovides a downlink or uplink transmission service to a plurality ofuser equipments. Different cells can be configured to providecorresponding bandwidths, respectively.

DL transport channels for transmitting data from a network to a userequipment include a BCH (broadcast channel) for transmitting a systeminformation, a PCH (paging channel) for transmitting a paging message, adownlink SCH (shared channel) for transmitting a user traffic or acontrol message and the like. DL multicast/broadcast service traffic ora control message may be transmitted on the DL SCH or a separate DL MCH(multicast channel). Meanwhile, UL transport channels for transmittingdata from a user equipment to a network include a RACH (random accesschannel) for transmitting an initial control message, an uplink SCH(shared channel) for transmitting a user traffic or a control message. Alogical channel, which is situated above a transport channel and mappedto the transport channel, includes a BCCH (broadcast channel), a PCCH(paging control channel), a CCCH (common control channel), a MCCH(multicast control channel), a MTCH (multicast traffic channel) and thelike.

FIG. 3 is a diagram for explaining physical channels used for 3GPPsystem and a general signal transmission method using the physicalchannels.

If a power of a user equipment is turned on or the user equipment entersa new cell, the user equipment may perform an initial cell search jobfor matching synchronization with an eNode B and the like [S301]. Tothis end, the user equipment may receive a primary synchronizationchannel (P-SCH) and a secondary synchronization channel (S-SCH) from theeNode B, may be synchronized with the eNode B and may then obtaininformation such as a cell ID and the like. Subsequently, the userequipment may receive a physical broadcast channel from the eNode B andmay be then able to obtain intra-cell broadcast information. Meanwhile,the user equipment may receive a downlink reference signal (DL RS) inthe initial cell search step and may be then able to check a DL channelstate.

Having completed the initial cell search, the user equipment may receivea physical downlink shared control channel (PDSCH) according to aphysical downlink control channel (PDCCH) and an information carried onthe physical downlink control channel (PDCCH). The user equipment may bethen able to obtain a detailed system information [S302].

Meanwhile, if a user equipment initially accesses an eNode B or does nothave a radio resource for transmitting a signal, the user equipment maybe able to perform a random access procedure to complete the access tothe eNode B [S303 to S306]. To this end, the user equipment may transmita specific sequence as a preamble on a physical random access channel(PRACH) [S303/S305] and may be then able to receive a response messageon PDCCH and the corresponding PDSCH in response to the preamble[S304/S306]. In case of a contention based random access procedure(RACH), it may be able to additionally perform a contention resolutionprocedure.

Having performed the above mentioned procedures, the user equipment maybe able to perform a PDCCH/PDSCH reception [S307] and a PUSCH/PUCCH(physical uplink shared channel/physical uplink control channel)transmission [S308] as a general uplink/downlink signal transmissionprocedure. In particular, the user equipment receives a DCI (downlinkcontrol information) on the PDCCH. In this case, the DCI contains such acontrol information as an information on resource allocation to the userequipment. The format of the DCI varies in accordance with its purpose.

Meanwhile, control information transmitted to an eNode B from a userequipment via UL or the control information received by the userequipment from the eNode B includes downlink/uplink ACK/NACK signals,CQI (Channel Quality Indicator), PMI (Precoding Matrix Index), RI (RankIndicator) and the like. In case of 3GPP LTE system, the user equipmentmay be able to transmit the aforementioned control information such asCQI/PMI/RI and the like on PUSCH and/or PUCCH.

FIG. 4 is a diagram for a structure of a radio frame in LTE system.

Referring to FIG. 4, one radio frame has a length of 10 ms(327,200×T_(S)) and is constructed with 10 subframes in equal size. Eachof the subframes has a length of 1 ms and is constructed with two slots.Each of the slots has a length of 0.5 ms (15,360×T_(S)). In this case,T_(s) indicates a sampling time and is represented as T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (i.e., about 33 ns). The slot includes a pluralityof OFDM symbols in a time domain and also includes a plurality ofresource blocks (RBs) in a frequency domain. In the LTE system, oneresource block includes ‘12 subcarriers×7 or 6 OFDM symbols’. Atransmission time interval (TTI), which is a unit time for transmittingdata, can be determined by at least one subframe unit. Theaforementioned structure of a radio frame is just exemplary. And, thenumber of subframes included in a radio frame, the number of slotsincluded in a subframe and the number of OFDM symbols included in a slotmay be modified in various ways.

FIG. 5 is a diagram for showing an example of a control channel includedin a control region of a single subframe in a DL radio frame.

Referring to FIG. 5, a subframe consists of 14 OFDM symbols. Accordingto a subframe configuration, the first 1 to 3 OFDM symbols are used fora control region and the other 13˜11 OFDM symbols are used for a dataregion. In the diagram, R1 to R4 may indicate a reference signal(hereinafter abbreviated RS) or a pilot signal for an antenna 0 to 3.The RS is fixed as a constant pattern in the subframe irrespective ofthe control region and the data region. The control channel is assignedto a resource to which the RS is not assigned in the control region anda traffic channel is also assigned to a resource to which the RS is notassigned in the data region. The control channel assigned to the controlregion may include a physical control format indicator channel (PCFICH),a physical hybrid-ARQ indicator channel (PHICH), a physical downlinkcontrol channel (PDCCH), and the like.

The PCFICH (physical control format indicator channel) informs a userequipment of the number of OFDM symbols used for the PDCCH on everysubframe. The PCFICH is situated at the first OFDM symbol and isconfigured prior to the PHICH and the PDCCH. The PCFICH consists of 4resource element groups (REG) and each of the REGs is distributed in thecontrol region based on a cell ID (cell identity). One REG consists of 4resource elements (RE). The RE may indicate a minimum physical resourcedefined as ‘one subcarrier×one OFDM symbol’. The value of the PCFICH mayindicate the value of 1 to 3 or 2 to 4 according to a bandwidth and ismodulated into a QPSK (quadrature phase shift keying).

The PHICH (physical HARQ (hybrid-automatic repeat and request) indicatorchannel) is used for carrying HARQ ACK/NACK for an UL transmission. Inparticular, the PHICH indicates a channel to which DL ACK/NACKinformation is transmitted for UL HARQ. The PHICH consists of a singleREG and is scrambled cell-specifically. The ACK/NACK is indicated by 1bit and modulated into BPSK (binary phase shift keying). The modulatedACK/NACK is spread into a spread factor (SF) 2 or 4. A plurality ofPHICHs, which are mapped to a same resource, composes a PHICH group. Thenumber of PHICH, which is multiplexed by the PHICH group, is determinedaccording to the number of spreading code. The PHICH (group) is repeatedthree times to obtain diversity gain in a frequency domain and/or a timedomain.

The PDCCH (physical DL control channel) is assigned to the first n OFDMsymbol of a subframe. In this case, the n is an integer more than 1 andindicated by the PCFICH. The PDCCH consists of at least one CCE. ThePDCCH informs each of user equipments or a user equipment group of aninformation on a resource assignment of PCH (paging channel) and DL-SCH(downlink-shared channel), which are transmission channels, an uplinkscheduling grant, HARQ information and the like. The PCH (pagingchannel) and the DL-SCH (downlink-shared channel) are transmitted on thePDSCH. Hence, an eNode B and the user equipment transmit and receivedata via the PDSCH in general except a specific control information or aspecific service data.

Information on a user equipment (one or a plurality of user equipments)receiving data of PDSCH, a method of receiving and decoding the PDSCHdata performed by the user equipment, and the like is transmitted in amanner of being included in the PDCCH. For instance, assume that aspecific PDCCH is CRC masked with an RNTI (radio network temporaryidentity) called “A” and an information on data transmitted using aradio resource (e.g., frequency position) called “B” and a DCI formati.e., a transmission form information (e.g., a transport block size, amodulation scheme, coding information, and the like) called “C” istransmitted via a specific subframe. In this case, the user equipment ina cell monitors the PDCCH using the RNTI information of its own, ifthere exist at least one or more user equipments having the “A” RNTI,the user equipments receive the PDCCH and the PDSCH, which is indicatedby the “B” and the “C”, via the received information on the PDCCH.

FIG. 6 is a diagram for a structure of an uplink subframe used in LTEsystem.

Referring to FIG. 6, an UL subframe can be divided into a region towhich a physical uplink control channel (PUCCH) carrying controlinformation is assigned and a region to which a physical uplink sharedchannel (PUSCH) carrying a user data is assigned. A middle part of thesubframe is assigned to the PUSCH and both sides of a data region areassigned to the PUCCH in a frequency domain. The control informationtransmitted on the PUCCH includes an ACK/NACK used for HARQ, a CQI(channel quality indicator) indicating a DL channel status, an RI (rankindicator) for MIMO, an SR (scheduling request) corresponding to an ULresource allocation request, and the like. The PUCCH for a single UEuses one resource block, which occupies a frequency different from eachother in each slot within a subframe. In particular, 2 resource blocksassigned to the PUCCH are frequency hopped on a slot boundary. Inparticular, FIG. 6 shows an example that the PUCCHs satisfyingconditions (e.g., m=0, 1, 2, 3) are assigned to a subframe.

In the following description, MIMO system is explained. The MIMO(multiple-input multiple-output) is a method using a plurality oftransmitting antennas and a plurality of receiving antennas. Theefficiency in transmitting and receiving data may be enhanced by theMIMO. In particular, by using a plurality of the antennas at atransmitting end or a receiving end in a radio communication system, itmay be able to increase a capacity and enhance performance. In thefollowing description, the MIMO may be called a ‘multi antenna’.

In the multiple antenna technology, it may not depend on a singleantenna path to receive a whole message. Data is completed in a mannerof combining data fragments received from many antennas in one place inthe multiple antenna technology instead. When the multiple antennatechnology is used, a data transmission speed may be enhanced in a cellarea having a specific size or a system coverage may be enlarged while aspecific data transmission speed is secured. And, this technology iswidely used in a mobile communication terminal, a relay station, and thelike. According to the multiple antenna technology, a throughputlimitation of a single antenna used by a conventional technology in amobile communication can be overcome.

A block diagram of a general multi-antenna (MIMO) communication systemis depicted in FIG. 7.

N_(T) number of transmitting antenna is installed in a transmitting endand N_(R) number of receiving antenna is installed in a receiving end.As described in the above, in case that both the transmitting end andthe receiving end use plural number of antennas, a theoretical channeltransmission capacity is increased compared to a case that the pluralnumber of antennas are only used for either the transmitting end or thereceiving end. The increase of the channel transmission capacity isproportional to the number of antenna. Thus, a transfer rate is enhancedand frequency efficiency is enhanced. If a maximum transfer rate isrepresented as R_(o) in case of using a single antenna, the transferrate using multiple antennas can be theoretically increased as much asthe maximum transfer rate R_(o) multiplied by a rate of increase asshown in the following Formula 1. In this case, the R_(i) is a smallervalue of the N_(T) and the N_(R).R _(i)=min(N _(T) ,N _(R))  [Formula 1]

For instance, MIMO communication system using 4 transmitting antennasand 4 receiving antennas may be able to theoretically obtain thetransfer rate of 4 times of a single antenna system. After thetheoretical capacity increase of the multi-antenna system is proved inthe mid-90s, various technologies for practically enhancing a datatransmission rate have been actively studied up to date and severaltechnologies among them are already reflected in such a various wirelesscommunication standard as a 3^(rd) generation mobile communication, anext generation wireless LAN and the like.

If we look at the research trend related to the multi-antenna until now,many active researches have been performed for such a study of variouspoints of view as a study on information theory related to amulti-antenna communication capacity calculation in various channelenvironments and multiple access environment, a study on a radio channelmeasurement and model deduction of the multi-antenna system, a study ona space-time signal processing technology for enhancing a transmissionreliability and a transmission rate, and the like.

In case of mathematically modeling a communication method of themulti-antenna system in order to explain it with more specific way, itcan be represented as follows. As shown in FIG. 7, assume that thereexist N_(T) number of transmitting antenna and N_(R) number of receivingantenna. First of all, if we look into a transmission signal, since themaximum number of information capable of being transmitted is N_(T) incase that there exists N_(T) number of transmitting antenna,transmission information can be represented as a vector in the followingFormula 2.s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Formula 2]

Meanwhile, for each of the transmission informations s₁, s₂, . . . ,s_(N) _(T) , a transmit power may be differentiated according to theeach of the transmission informations. In this case, if each of thetransmit powers is represented as P₁, P₂, . . . , P_(N) _(T) , transmitpower-adjusted transmission information can be represented as a vectorin the following Formula 3.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Formula 3]

And, if ŝ is represented using a diagonal matrix P, it can berepresented as a following Formula 4.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Meanwhile, let's consider a case that the N_(T) number of transmissionsignal x₁, x₂, . . . , x_(N) _(T) , which is practically transmitted, isconfigured in a manner of applying a weighted matrix W to the adjustedinformation vector Ŝ. In this case, the weighted matrix performs a roleof distributing the transmission information to each of the antennasaccording to the situation of the transmission channel and the like. Thetransmission signal x₁, x₂, . . . , x_(N) _(T) can be represented usinga vector X in the following Formula 5. In this case, W_(ij) means aweighting between an i^(th) transmitting antenna and j^(th) information.The W is called the weighted matrix or a precoding matrix.

$\begin{matrix}\begin{matrix}{X = {\quad\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix}}} \\{= {\begin{bmatrix}w_{11} & w_{12} & \cdots & w_{1N_{T}} \\w_{21} & w_{22} & \cdots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \cdots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \cdots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}}} \\{= {W\hat{s}}} \\{= {WPs}}\end{matrix} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In general, a physical meaning of a rank of a channel matrix mayindicate a maximum number capable of transmitting different informationfrom each other in a given channel. Hence, since the rank of the channelmatrix is defined by a minimum number of the numbers of row or columnindependent from each other, the rank of the matrix is configured not tobe greater than the number of the row or the column. For instance, therank of a channel matrix H (rank (H)) is limited as shown in Formula 6.rank(H)≦min(N _(T) ,N _(R))  [Formula 6]

And, let's define each of the informations different from each other,which are transmitted using a multi-antenna technology, as a transportstream or simply a stream. The stream can be named a layer. Then, thenumber of the transport stream is naturally configured not to be greaterthan the rank of the channel, which is a maximum number capable oftransmitting informations different from each other. Hence, the channelmatrix H can be represented as Formula 7 in the following.# of streams≦rank(H)≦min(N _(T) ,N _(R))  [Formula 7]

In this case, ‘# of streams’ indicates the number of streams. Meanwhile,in this case, it should be cautious that one stream can be transmittedvia more than one antenna.

Various methods making one or more streams correspond to many antennasmay exist. These methods can be described in accordance with the kind ofthe multi-antenna technology in the following description. A case oftransmitting one stream via many antennas may be called a spacediversity scheme and a case of transmitting many streams via manyantennas may be called a space multiplexing scheme. Naturally, a hybridform of the space diversity and the space multiplexing is alsoavailable.

Meanwhile, it is expected that a LTE-A system, which is a standard of anext generation mobile communication system, will support a CoMP(coordinated multi point) transmission method, which is not supported bythe conventional standard, to enhance a data transmission rate. In thiscase, the CoMP transmission method is a transmission method for two ormore base stations or cells to communicate with the user equipment in amanner of cooperating with each other to enhance a communicationperformance between the user equipment situated at a radio shadow zoneand the base station (a cell or a sector).

The CoMP transmission method can be classified into a join processing(CoMP joint processing, CoMP-JP) method in the form of a cooperativeMIMO via data sharing and a coordinated scheduling/beamforming(CoMP-coordinated scheduling/beamforming, CoMP-CS/CB) method.

According to the joint processing (CoMP-JP) method in DL, a userequipment may be able to instantaneously receive data simultaneouslyfrom each of the base stations performing the CoMP transmission method.And, a reception performance can be enhanced in a manner of combiningthe signals received from each of the base stations (Joint Transmission(JT)). And, it is also possible to consider a method of transmitting adata to the user equipment on a specific timing by one of the basestations performing the CoMP transmission method (Dynamic PointSelection (DPS)). On the other hand, according to the coordinatedscheduling/beamforming method (CoMP-CS/CB), the user equipment may beable to instantaneously receive data from a single base station via abeamforming.

According to the joint processing (CoMP-JP) method in UL, each of thebase stations may be able to simultaneously receive PUSCH signal fromthe user equipment (Joint Reception (JR)). On the other hand, accordingto the coordinated scheduling/beamforming method (CoMP-CS/CB), only asingle base station may be able to receive the PUSCH. In this case, thedecision to use the coordinated scheduling/beamforming method isdetermined by the coordinating cells (or base stations).

In the following description, a reference signal is explained in moredetail.

In general, a reference signal, which is already known to both atransmitting end and a receiving end, is transmitted from thetransmitting end to the receiving end together with data to measure achannel. The reference signal plays not only a role of measuring achannel but also a role of making a demodulation process to be performedin a manner of informing the receiving end of a modulation scheme. Thereference signal is classified into a dedicated reference signal (DRS)used for an eNB and a specific user equipment (i.e., UE-specificreference signal) and a cell-specific reference signal used for all UEsin a cell (i.e., common reference signal or cell specific RS (CRS)). Thecell-specific reference signal includes a reference signal used forreporting CQI/PMI/RI to an eNB in a manner of measuring CQI/PMI/RI in auser equipment. This sort of reference signal is called a CSI-RS(channel state information-RS).

FIG. 8 and FIG. 9 are diagrams of a structure of a reference signal inLTE system supportive of downlink transmission using 4 antennas. Inparticular, FIG. 8 shows a case of a normal cyclic prefix and FIG. 9shows a case of an extended cyclic prefix.

Referring to FIG. 8 and FIG. 9, 0 to 3 written on a grid may mean theCRS (common reference signal), which is a cell-specific referencesignal, transmitted for the channel measurement and the datademodulation in a manner of corresponding to antenna port 0 to 3,respectively. The cell-specific reference signal CRS can be transmittedto a user equipment via the control information region as well as thedata information region.

And, ‘D’ written on the grid may mean a downlink DM-RS (demodulationRS), which is a user-specific RS. The DM-RS supports a single antennaport transmission via the data region, i.e., the PDSCH. The userequipment is signaled whether the DM-RS, which is the userequipment-specific RS, exists or not via an upper layer. FIG. 8 and FIG.9 show an example of the DM-RS corresponding to an antenna port 5. TheDM-RSs corresponding to an antenna port 7 to 14, i.e., total 8 antennaports, are also defined by 3GPP standard document 36.211.

FIG. 10 is a diagram for an example of assigning a downlink DM-RSdefined by a current 3GPP standard document.

Referring to FIG. 10, DM-RSs corresponding to antenna ports {7, 8, 11,13} are mapped to a DM-RS group 1 using a sequence according to anantenna port and DM-RSs corresponding to antenna ports {9, 10, 12, 14}are mapped to a DM-RS group 2 using a sequence according to an antennaport as well.

Meanwhile, the aforementioned CSI-RS is proposed to perform channelmeasurement for PDSCH irrespective of a CRS. Unlike the CRS, the CSI-RScan be defined by maximum 32 resource configurations different from eachother to reduce inter-cell interference (ICI) in a multicellenvironment.

CSI-RS (resource) configuration varies according to the number ofantenna ports. A CSI-RS is configured to be transmitted by different(resource) configurations between neighboring cells. Unlike the CRS, theCSI-RS supports maximum 8 antenna ports. According to 3GPP standarddocument, total 8 antenna ports (antenna port 15 to antenna port 22) areassigned as the antenna port for the CSI-RS. FIG. 11 is a diagram for anexample of a CSI-RS (resource) configuration #0 in case of a normal CPamong CSI-RS configurations defined by a current 3GPP standard document.

Meanwhile, as various devices requiring high data transmission capacityare emerged and disseminated, data requisites for a cellular network arerapidly increasing in a current wireless communication environment. Inorder to satisfy high data requisite, communication technologies aredeveloping to a carrier aggregation technology for efficiently usingmore frequency bands, a multi-antenna technology used for increasingdata capacity in a limited frequency, a multi-base station cooperationtechnology, and the like and the communication environment is evolvingin a manner that density of an accessible node is growing in thevicinity of a user.

A system equipped with the node of high density may have higher systemperformance by means of cooperation between nodes. Compared to a nodeoperating as an independent base station without cooperation, theaforementioned scheme may have superior performance.

FIG. 12 is a diagram for an example of a multi node system in a nextgeneration communication system.

Referring to FIG. 12, if an individual node operates as a part ofantenna group of a cell in a manner that a controller managestransmission and reception of all nodes, it may correspond to adistributed multi node system (DMNS) that forms a single cell. In thiscase, each of the individual nodes may receive a separate node ID or mayoperate as a part of antenna within the cell without a separate Node ID.Yet, if nodes have a cell identifier (ID) different from each other, itmay correspond to a multi-cell system. If a multi cell is configured bya duplicated form according to coverage, this is called a multi-tiernetwork.

Meanwhile, a Node-B, an eNode-B, a PeNB, a HeNB, an RRH (remote radiohead), a relay, a distributed antenna, and the like may become a nodeand at least one antenna is installed in a node. A node is also called atransmission point. In general, a node indicates an antenna group apartfrom each other more than a prescribed space, the present inventiondefines and applies a node as a random antenna group irrespective of aspace.

With the help of the introduction of the aforementioned multi-nodesystem, application of various communication schemes is enabled andchannel quality enhancement can be performed. Yet, in order to apply theaforementioned MIMO scheme and inter-cell cooperation communicationscheme to a multi-node environment, an introduction of a new controlchannel is required. To this end, a control channel considered as thenewly introduced control channel, which corresponds to an E-PDCCH(enhanced-PDCCH), is under discussion. This channel is determined to beassigned to a data region (hereinafter described as PDSCH region)instead of a legacy control region (hereinafter described as PDCCHregion). Consequently, control information on a node can be transmittedaccording to each UE via the E-PDCCH. Hence, a problem of shortage ofthe legacy PDCCH region can be solved as well. For reference, theE-PDCCH is not provided to a legacy UE. Instead, an LTE-A UE can receivethe E-PDCCH only.

FIG. 13 is a diagram for an example of E-PDCCH and PDSCH scheduled byE-PDCCH.

Referring to FIG. 13, E-PDCCH can be used in a manner of defining a partof PDSCH region, which is generally transmitting data. A UE shouldperform a blind decoding process to detect presence or non-presence ofthe E-PDCCH in the UE. The E-PDCCH performs a scheduling operation(i.e., PDSCH, PUSCH control) identical to that of a legacy PDCCH. Yet,if the number of such a UE accessed a node as an RRH increases, moreE-PDCCHs are assigned to the PDSCH region. Hence, the number of blinddecoding, which should be performed by the UE, increases and complexitymay increase as well.

In the following description, an example for a transmission mode of adownlink data channel is described.

Currently, 3GPP LTE standard document, specifically, 3GPP TS 36. 213document defines a transmission mode of a downlink data channel as shownin Table 1 and Table 2 in the following. The transmission mode is set toa user equipment via an upper layer signaling, i.e., RRC signaling.

TABLE 1 Transmission Transmission scheme of PDSCH mode DCI formatcorresponding to PDCCH Mode 1 DCI format 1A Single-antenna port, port 0DCI format 1 Single-antenna port, port 0 Mode 2 DCI format 1A Transmitdiversity DCI format 1 Transmit diversity Mode 3 DCI format 1A Transmitdiversity DCI format 2A Large delay CDD or Transmit diversity Mode 4 DCIformat 1A Transmit diversity DCI format 2 Closed-loop spatialmultiplexing or Transmit diversity Mode 5 DCI format 1A Transmitdiversity DCI format 1D Multi-user MIMO Mode 6 DCI format 1A Transmitdiversity DCI format 1B Closed-loop spatial multiplexing using a singletransmission layer Mode 7 DCI format 1A If the number of PBCH antennaports is one, Single-antenna port, port 0 is used, otherwise Transmitdiversity DCI format 1 Single-antenna port, port 5 Mode 8 DCI format 1AIf the number of PBCH antenna ports is one, Single-antenna port, port 0is used, otherwise Transmit diversity DCI format 2B Dual layertransmission, port 7 and 8 or single-antenna port, port 7 or 8 Mode 9DCI format 1A Non-MBSFN subframe: If the number of PBCH antenna ports isone, Single- antenna port, port 0 is used, otherwise Transmit diversityMBSFN subframe: Single-antenna port, port 7 DCI format 2C Up to 8 layertransmission, ports 7-14 or single-antenna port, port 7 or 8 Mode 10 DCIformat 1A Non-MBSFN subframe: If the number of PBCH antenna ports isone, Single- antenna port, port 0 is used, otherwise Transmit diversityMBSFN subframe: Single-antenna port, port 7 DCI format 2D Up to 8 layertransmission, ports 7-14 or single-antenna port, port 7 or 8

TABLE 2 Transmission Transmission scheme of PDSCH mode DCI formatcorresponding to PDCCH Mode 1 DCI format 1A Single-antenna port, port 0DCI format 1 Single-antenna port, port 0 Mode 2 DCI format 1A Transmitdiversity DCI format 1 Transmit diversity Mode 3 DCI format 1A Transmitdiversity DCI format 2A Transmit diversity Mode 4 DCI format 1A Transmitdiversity DCI format 2 Transmit diversity Mode 5 DCI format 1A Transmitdiversity Mode 6 DCI format 1A Transmit diversity Mode 7 DCI format 1ASingle-antenna port, port 5 DCI format 1 Single-antenna port, port 5Mode 8 DCI format 1A Single-antenna port, port 7 DCI format 2BSingle-antenna port, port 7 or 8 Mode 9 DCI format 1A Single-antennaport, port 7 DCI format 2C Single-antenna port, port 7 or 8, Mode 10 DCIformat 1A Single-antenna port, port 7 DCI format 2D Single-antenna port,port 7 or 8,

Referring to Table 1 and Table 2, current 3GPP LTE standard documentincludes a downlink control information (DCI) format, which is definedaccording to a type of RNTI masked on PDCCH. In particular, in case of aC-RNTI and an SPS C-RNTI, a transmission mode and a DCI formatcorresponding to the transmission mode (i.e., a transmission mode-basedDCI format) are included in the document. And, a DCI format 1A for aFall-back mode, which is capable of being applied irrespective of eachtransmission mode, is defined in the document. Table 1 shows an exampleof a case that a type of RNTI masked on PDCCH corresponds to a C-RNTIand Table 2 shows an example of a case that the type of RNTI masked onPDCCH corresponds to an SPS C-RNTI.

As an example of an operation of a transmission mode, referring to Table1, if a user equipment performs a blind decoding on PDCCH masked withC-RNTI and then detects a DCI format 1B, the user equipment decodesPDSCH in an assumption that the PDSCH has been transmitted with aclosed-loop spatial multiplexing scheme using a single transmissionlayer.

In Table 1 and Table 2, a transmission mode 10 indicates a downlink datachannel transmission mode of the aforementioned CoMP transmissionmethod. For instance, referring to Table 1, if a user equipment performsa blind decoding on PDCCH masked with C-RNTI and then detects a DCIformat 2D, the user equipment decodes PDSCH in an assumption that thePDSCH has been transmitted with a multi-layer transmission scheme basedon antenna port 7 to 14, i.e., DM-RS. Or, the user equipment decodesPDSCH in an assumption that the PDSCH has been transmitted with a singleantenna transmission scheme based on DM-RS antenna port 7 or 8.

On the contrary, if the user equipment performs blind decoding on PDCCHmasked with C-RNTI and then detects a DCI format 1A, a transmission modevaries according to whether a corresponding subframe corresponds to anMBSFN subframe. For instance, if the corresponding subframe correspondsto a non-MBSFN subframe, the user equipment decodes PDSCH in anassumption that the PDSCH has been transmitted with a single antennatransmission scheme based on a CRS of an antenna port 0 or a CRS-basedtransmit diversity scheme. And, if the corresponding subframecorresponds to an MBSFN subframe, the user equipment decodes the PDSCHin an assumption that the PDSCH has been transmitted with a singleantenna transmission based on a DM-RS of an antenna port 7.

In the following, QCL (Quasi Co-Location) between antenna ports isexplained.

QCL between antenna ports indicates that all or a part of large-scaleproperties of a signal (or a radio channel corresponding to acorresponding antenna port) received by a user equipment from a singleantenna port may be identical to large-scale properties of a signal (ora radio channel corresponding to a corresponding antenna port) receivedfrom a different single antenna port. In this case, the larger-scaleproperties may include Doppler spread related to frequency offset,Doppler shift, average delay related to timing offset, delay spread andthe like. Moreover, the larger-scale properties may include average gainas well.

According to the aforementioned definition, a user equipment cannotassume that the large-scale properties are identical to each otherbetween antenna ports not in the QCL, i.e., NQCL (Non Quasi co-located)antenna ports. In this case, the user equipment should independentlyperform a tracking procedure to obtain frequency offset, timing offsetand the like according to an antenna port.

On the contrary, the user equipment can perform following operationsbetween antenna ports in QCL.

1) The user equipment can identically apply power-delay profile for aradio channel corresponding to a specific antenna port, delay spread,Doppler spectrum and Doppler spread estimation result to a Wiener filterparameter, which is used for estimating a channel for a radio channelcorresponding to a different antenna port, and the like.

2) After obtaining time synchronization and frequency synchronizationfor the specific antenna port, the user equipment can apply identicalsynchronization to a different antenna port as well.

3) The user equipment can calculate an average value of RSRP (referencesignal received power) measurement values of each of the antenna portsin QCL to obtain average gain.

For instance, having received DM-RS based downlink data channelscheduling information (e.g., DCI format 2C) via PDCCH (or E-PDCCH), theuser equipment performs channel estimation for PDSCH via a DM-RSsequence indicated by the scheduling information and may be then able toperform data demodulation.

In this case, if a DM-RS antenna port used for demodulating a downlinkdata channel and a CRS antenna port of a serving cell are in QCL, whenthe user equipment performs a channel estimation via the DM-RS antennaport, the user equipment can enhance reception capability of the DM-RSbased downlink data channel in a manner of applying large-scaleproperties of a radio channel estimated from a CRS antenna port of theuser equipment as it is.

Similarly, if a DM-RS antenna port used for demodulating a downlink datachannel and a CSI-RS antenna port of a serving cell are in QCL, when theuser equipment perform a channel estimation via the DM-RS antenna port,the user equipment can enhance reception capability of the DM-RS baseddownlink data channel in a manner of applying large-scale properties ofa radio channel estimated from a CSI-RS antenna port of the serving cellas it is.

Based on the aforementioned contents, a method of receiving a downlinkdata channel in a multicell-based wireless communication system and anapparatus therefor according to the present invention are explained inthe following. In particular, the present invention proposes a method ofcalculating or assuming large-scale properties for each of radiochannels from a CoMP set, i.e., TPs participating in CoMP and a methodof obtaining synchronization in order for a user equipment to receive adownlink signal in the multicell-based wireless communication system.

The user equipment can obtain synchronization via a primarysynchronization signal (PSS) and a secondary synchronization signal(SSS) periodically transmitted from TPs within a CoMP set. After aninitial synchronization is obtained, the user equipment calculatestiming offset (delay spread and average delay), frequency offset(Doppler spread and Doppler shift) and the like by consistently trackinga reference signal and can maintain the synchronization. As a referencesignal for the tracking, a CSI-RS, a CRS or the like can be used. Theuser equipment maintains the synchronization with TP using informationincluding the timing offset, the frequency offset and the likecalculated by the tracking and can demodulate PDSCH. In this case, asdefined in LTE system, demodulation of the PDSCH means DM-RS-baseddemodulation. Using the information including the timing offset, thefrequency offset and the like may mean that an antenna port of a DM-RSand an antenna port of a CSI-RS or a CRS, which is a reference signalused for the tracking, are in QCL.

FIG. 14 is a diagram of an example for a user equipment to perform atracking to obtain synchronization in a multicell-based wirelesscommunication system.

Referring to FIG. 14, a user equipment operating in a CoMP mode, i.e.,the user equipment operating in the aforementioned PDSCH transmissionmode 10 can perform tracking for TPs within a CoMP set as well as acurrent serving cell (or a serving TP). FIG. 14 shows an example thatthe user equipment receives a reference signal from a TP A and areference signal from a TP B to calculate timing offset Δt and frequencyoffset Δf.

In particular, in case that the TPs within the CoMP set use an identicalcell identifier, the user equipment can calculate the timing offset Δtand the frequency offset Δf of each TP in a manner of configuring CSI-RSresources different from each other for every TP and tracking each ofthe CSI-RSs. On the contrary, in case that the TPs within the CoMP setuse cell identifiers different from each other, the user equipment cancalculate the timing offset Δt and the frequency offset Δf of each TP ina manner of tracking a CRS differently configured for every TP by adifferent method except the method of configuring the CSI-RS resourcesdifferent from each other for every TP.

Meanwhile, if there exist a plurality of information including timingoffset and frequency offset which is calculated by the user equipment bytracking a reference signal and it is not able to know information on aTP from which a currently received PDSCH is transmitted, the UE is notable to know information on timing offset and frequency offset becominga criterion of performing synchronization acquisition and DM-RS basedPDSCH demodulation. In particular, the use equipment is not able to knowan antenna port of a reference signal, which is in QCL with an antennaport of a DM-RS for the currently received PDSCH.

As a method of selecting an appropriate timing offset and a frequencyoffset from a plurality of the timing offsets and frequency offsets, itmay consider following methods.

1) First of all, a UE may anticipate that a scheduler schedules a TP,which has transmitted a strongest reference signal among a plurality ofreference signals tracked by the UE, to transmit PDSCH. Hence, the UEperforms the synchronization acquisition and the DM-RS based PDSCHdemodulation using the offset information which is calculated bytracking the reference signal measured as the strongest signal. Inparticular, the UE may assume that the antenna port of the DM-RS for thecurrently received PDSCH and the antenna port of the reference signalmeasured as the strongest signal are in QCL.

2) As a different method, a UE may anticipate that PDSCH issimultaneously transmitted from a plurality of TPs among TPs includingoffsets different from each other within a CoMP set. In this case, theUE can calculate an average value of the offsets calculated from aplurality of the TPs. The UE performs the synchronization acquisitionand the DM-RS based PDSCH demodulation using the average offset value.In this case, it may assume that the antenna port of the DM-RS for thecurrently received PDSCH and a virtual specific antenna port are in QCL.And, it may also understand that a result of tracking the virtualspecific antenna port corresponds to the average offset value.

3) As a further different method, a network (e.g., a serving cell) maydirectly inform a UE of offset information to be used for PDSCHreception and demodulation. The information is semi-statically deliveredto the UE via such an upper layer signaling as an RRC layer or can bedynamically delivered via such a physical layer signal as PDCCH. Theoffset information may correspond to an index or an antenna port of areference signal set to a TP configured to transmit PDSCH amongreference signals tracked by the UE. The UE performs the synchronizationacquisition and the DM-RS based PDSCH demodulation using specific offsetinformation corresponding to a result of tracking a reference signalindicated by the network among a plurality of offset informationcalculated by tracking a plurality of reference signals. In particular,it may assume that the antenna port of the DM-RS for the currentlyreceived PDSCH and the antenna port of the reference signal indicated bythe network are in QCL.

When a TP transmits a signal, the TP can transmit the signal in a mannerof applying scrambling to the signal with a scrambling code todistinguish the signal from a signal transmitted by a different TP. Whena UE receives the scrambled signal, the UE can restores the signal byperforming a reverse scrambling procedure using a code identical to acode used by the TP.

The scrambling code is a common name for promised information deliveredto the UE from the TP in order for the UE to precisely perform PDSCHdemodulation. The scrambling code is not limited to a specificsignaling. For instance, the scrambling code may correspond to ascrambling sequence put on PDSCH to protect data or reference signalconfiguration information such as an RE position, sequence and the likeof a CRS or a DM-RS necessary for performing PDSCH demodulation.Moreover, the scrambling code may correspond to an index of a componentcarrier to which the PDSCH is transmitted in case of applying carrieraggregation scheme.

Hence, a scrambling code used for transmitting PDSCH may vary accordingto every TP within a CoMP set. In particular, in case that a TPtransmitting PDSCH is dynamically changing such as a dynamic TPselection (DPS) scheme, a network should dynamically inform a UE of aprecise scrambling code necessary for demodulating PDSCH via PDCCH.Hence, the network can inform the UE of the scrambling code used by eachTP within the CoMP set to transmit PDSCH and reference signalconfiguration information of the corresponding TP in advance. Theinformation can be semi-statically transmitted via such an upper layersignaling as an RRC layer signal. Table 3 in the following is an exampleof the scrambling code of the TP and the reference signal configurationinformation informed to the UE by the network.

TABLE 3 Configuration Scrambling code Reference signal 1 SCID1 RS-A 2SCID2 RS-B 3 SCID3 RS-C . . . . . . . . .

The network can make each of TPs use configurations different from eachother, respectively among the configurations depicted in Table 3. EachTP uses a scrambling code and a reference signal of a promisedcombination according to a determined combination shown in Table 3.

Assume that a reference signal depicted in Table 3 corresponds to aCSI-RS. Since a UE stores such information shown in Table 3 in advance,although the UE receives scrambling code indicator (SCID #) informationfrom the network only, the UE is able to know how a CSI-RS resource,which is used by a TP transmitting PDSCH, is configured, which CSI-RScan be assumed for QCL with a CRS or a DM-RS necessary for performingPDSCH demodulation and the like. Hence, the UE can performsynchronization acquisition and PDSCH demodulation using a plurality ofoffset information calculated by CSI-RS tracking without a separatesignaling from the network for synchronization acquisition.

FIG. 15 is a diagram of an example for a user equipment to perform areference signal tracking according to embodiment of the presentinvention. As mentioned in the foregoing description, the UE is trackinga reference signal A (RS-A) set to the UE and a reference signal B(RS-B) and can obtain each offset information (i.e., timing offset andfrequency offset information based on the reference signal A, timingoffset and frequency offset information based on the reference signalB). In this case, the UE is unable to know which timing offset andfrequency offset are should be used to obtain synchronization among thetwo timing offsets and the frequency offsets. In the following, forclarity, the reference signal A and the reference signal B are called aCSI-RS A and a CSI-RS B, respectively.

Referring to FIG. 15, a network can inform a UE of a SCID 1 asinformation necessary for demodulating PDSCH while transmitting thePDSCH via a TP-A. In this case, as mentioned in the foregoingdescription, the SCID 1 may correspond to a scrambling sequence, DM-RSresource configuration information, or CRS resource configurationinformation.

In this case, although the UE is unable to know that a TP actuallytransmitting the PDSCH corresponds to the TP-A, the UE can performsynchronization acquisition and PDSCH demodulation with offsetcalculated by tracking a CSI-RS A via a pre-stored scrambling code andreference signal configuration information depicted in Table 3. Inparticular, the UE can assume that an antenna port of a DM-RS or a CRSfor a currently received PDSCH and an antenna port of the CSI-RS A arein QCL.

FIG. 16 is a diagram of a different example for a user equipment toperform a reference signal tracking according to embodiment of thepresent invention.

Referring to FIG. 16, a network can inform a UE of a SCID 2 asinformation necessary for demodulating PDSCH while transmitting thePDSCH via a TP-B. In this case, although the UE is unable to know that aTP actually transmitting the PDSCH corresponds to the TP-B, the UE canperform synchronization acquisition and PDSCH demodulation with offsetcalculated by tracking a CSI-RS B via a pre-stored scrambling code andreference signal configuration information depicted in Table 3. Inparticular, the UE can assume that an antenna port of a DM-RS or a CRSfor a currently received PDSCH and an antenna port of the CSI-RS B arein QCL.

In the following, a method for a network to inform offset information tobe used by a UE to receive and demodulate DM-RS (or CRS) based PDSCH,i.e., a method of signaling information on an antenna port where QCLassumption is feasible is explained in detail.

And, for clarity, assume a case that PDSCH is transmitted anddemodulated based on a DM-RS and an antenna port being QCL with anantenna port of the DM-RS is signaled in the following signalingmethods. Yet, it is apparent that the signaling methods can also beapplied to a case that the PDSCH is transmitted and demodulated based ona CRS.

<Signaling Method 1>

When a UE receives scheduling information of a DM-RS based PDSCH fromPDCCH or E-PDCCH, it may consider a method of dynamically signalingwhether a corresponding DM-RS antenna port(s) and a different referencesignal (e.g., a CRS of a serving cell, a different CSI-RS or the like)are in QCL.

A) First of all, the present invention proposes to define signaling of 1bit long and dynamically signal whether a QCL assumption with adifferent reference signal (i.e., a CRS of a serving cell, a differentCSI-RS or the like) is feasible. By doing so, when a CoMP DPS scheme isapplied, if a DM-RS based PDSCH is transmitted from a TP where the QCLassumption is feasible, demodulation capability of the DM-RS based PDSCHcan be enhanced in a manner of transmitting an indicator indicating thatQCL assumption with the different reference signal is feasible togetherwith scheduling information of the DM-RS based PDSCH.

B) As a different method, it may consider a method of semi-staticallyconfiguring QCL information between a CSI-RS (or, a CRS) and a DM-RS toa plurality of states via RRC signaling and the like and a method ofindicating one of a plurality of the states in case of transmittingscheduling information of a DM-RS based PDSCH.

For instance, if an indicator of 2 bits is defined to indicate a stateof scheduling information of a DM-RS based PDSCH, each state can bedefined as depicted in Table 4 and Table 5.

TABLE 4 00 NQCL 01 CRS of serving cell 10 1^(st) Set of QCL pair(configured by RRC layer) 11 2^(nd) Set of QCL pair (configured by RRClayer)

Referring to Table 4, if an indicator of 2-bit long included in thescheduling information of the DM-RS based PDSCH corresponds to “00”, theindicator indicates that a corresponding DM-RS cannot assume QCL withany reference signal, i.e., NQCL. If the indicator corresponds to “01”,it indicates that the corresponding DM-RS can assume QCL with a CRS of aserving cell. And, if the indicator corresponds to “10” or “11”, itindicates a QCL pair predefined via an RRC signaling. In this case, theQCL pair may indicate that QCL is applied between the DM-RS applied tothe corresponding PDSCH and a specific CSI-RS. For instance, “1^(st) Setof QCL pair” can be configured by QCL assumption between the DM-RSapplied to the corresponding PDSCH and a CSI-RS where a resourceconfiguration corresponds to #0. “2^(nd) Set of QCL pair” can beconfigured by QCL assumption between the DM-RS applied to thecorresponding PDSCH and a CSI-RS where a resource configurationcorresponds to #1.

TABLE 5 00 1^(st) Set of QCL pair (configured by RRC layer) 01 2^(nd)Set of QCL pair (configured by RRC layer) 10 3^(rd) Set of QCL pair(configured by RRC layer) 11 4^(th) Set of QCL pair (configured by RRClayer)

Referring to Table 5, if an indicator of 2-bit long included in thescheduling information of the DM-RS based PDSCH corresponds to “00” to“11”, all of the indicators indicate QCL pair predefined via RRCsignaling. In this case, the QCL pair may indicate that QCL is appliedbetween a DM-RS applied to a corresponding PDSCH and a specific CSI-RS.

C) As a further different method, among DM-RS configuration (orresource) included in the scheduling information (e.g., a DCI format 2Cdefined by LTE system) of the DM-RS based PDSCH, it may consider amethod of implicitly signaling whether there is QCL or NQCL between acorresponding DM-RS antenna port(s) and a different reference signal (aCRS or a CSI-RS of a serving cell) according to an nSCID value.

In particular, since the nSCID of a DM-RS sequence is defined by a valueof 0 or 1 in general, as depicted in Table 3, QCL or NQCL mappinginformation between DM-RS antenna port(s) and antenna port(s) of adifferent reference signal is configured in advance in the nSCID via anupper layer. In case that a UE receives the scheduling information ofthe DM-RS based PDSCH via PDCCH or E-PDCCH, the UE can applypreconfigured QCL/NQCL assumption between the DM-RS antenna port(s) andthe antenna port(s) of the different reference signal according to thenSCID value included in the scheduling information.

And, a DM-RS sequence scrambling seed value X may be mapped to the nSCIDvalue 0 and/or 1. According to whether the seed value X is identical toa PCI of a specific CRS antenna port(s), it may interpret whether QCKassumption is feasible. In particular, if the seed value X is identicalto the PCI of the specific CRS antenna port(s), it may interpret as theQCL assumption between the corresponding DM-RS antenna port(s) andcorresponding CRS antenna port(s) is feasible. If the seed value X isnot identical to the PCI of the specific CRS antenna port(s), it mayinterpret as NQCL is assumed between the corresponding DM-RS antennaport(s) and the corresponding CRS antenna port(s).

Similarly, according to whether the seed value X is identical to aCSI-RS sequence scrambling seed value Y of a specific CSI-RS antennaport(s), it may interpret whether QCK assumption is feasible. Inparticular, if the seed value X is identical to the seed value Y, it mayinterpret as the QCL assumption between the corresponding DM-RS antennaport(s) and corresponding CSI-RS antenna port(s) is feasible. If theseed value X is not identical to the seed value Y, it may interpret asNQCL is assumed between the corresponding DM-RS antenna port(s) and thecorresponding CSI-RS antenna port(s).

<Signaling Method 2>

a) Meanwhile, in the foregoing description, it has been explained that aDCI format for a fallback mode is defined as downlink controlinformation for a specific transmission mode. Unlike a general DCIformat, since the DCI format for the fallback mode, i.e., a DCI format1A is very limitative in defining a new field, when the DCI format 1A isreceived as scheduling information of the DM-RS based PDSCH, it isnecessary to consider a different method for applying QCL assumptionbetween a DM-RS and a different reference signal.

For instance, when a transmission mode 10 is configured and schedulinginformation of PDSCH is received by the DCI format 1A in an MBSFNsubframe, as defined in Table 1, a UE should receive the PDSCH based ona specific DM-RS antenna port (e.g., DM-RS antenna port 7 in Table 1).In this case, the UE may fixedly operate to make QCL assumption to bealways feasible between the DM-RS antenna port 7 and a CRS antennaport(s) of a serving cell (or a specific CSI-RS antenna port(s)).

b) Or, whether to apply QCL assumption can be determined according to atype of a search space in which scheduling information of PDSCH (inwhich QCL information is not included) is detected. For instance, if thescheduling information is detected in a common search space (CSS), itmay interpret as QCL assumption is always feasible between thecorresponding DM-RS antenna port(s) and CRS antenna port(s) of a servingcell of the DM-RS antenna port(s). On the contrary, if the schedulinginformation is detected in a UE-specific search space (USS), it mayinterpret as there exist a NQCL relation between the DM-RS antennaport(s) and an antenna port of a different reference signal.

c) There may exist a hybrid form of the aforementioned a) and b). Forinstance, in case of receiving a DCI format 1A in the CSS in an MBSFNsubframe, it may interpret as QCL assumption is feasible between thecorresponding DM-RS antenna port and CRS antenna port(s) of a servingcell (or a specific CSI-RS antenna port(s)). In case of receiving theDCI format 1A in the USS in the MBSFN subframe, it may interpret as QCLassumption is feasible between the corresponding DM-RS antenna port andan antenna port of a different reference signal.

FIG. 17 is a block diagram for an example of a communication deviceaccording to one embodiment of the present invention.

Referring to FIG. 17, a communication device 1700 may include aprocessor 1710, a memory 1720, an RF module 1730, a display module 1740,and a user interface module 1750.

Since the communication device 1700 is depicted for clarity ofdescription, prescribed module(s) may be omitted in part. Thecommunication device 1700 may further include necessary module(s). And,a prescribed module of the communication device 1700 may be divided intosubdivided modules. A processor 1710 is configured to perform anoperation according to the embodiments of the present inventionillustrated with reference to drawings. In particular, the detailedoperation of the processor 1710 may refer to the former contentsdescribed with reference to FIG. 1 to FIG. 16.

The memory 1720 is connected with the processor 1710 and stores anoperating system, applications, program codes, data, and the like. TheRF module 1730 is connected with the processor 1710 and then performs afunction of converting a baseband signal to a radio signal or a functionof converting a radio signal to a baseband signal. To this end, the RFmodule 1730 performs an analog conversion, amplification, a filtering,and a frequency up conversion, or performs processes inverse to theformer processes. The display module 1740 is connected with theprocessor 1710 and displays various kinds of informations. And, thedisplay module 1740 can be implemented using such a well-known componentas an LCD (liquid crystal display), an LED (light emitting diode), anOLED (organic light emitting diode) display and the like, by which thepresent invention may be non-limited. The user interface module 1750 isconnected with the processor 1710 and can be configured in a manner ofbeing combined with such a well-known user interface as a keypad, atouchscreen and the like.

The above-described embodiments correspond to combinations of elementsand features of the present invention in prescribed forms. And, therespective elements or features may be considered as selective unlessthey are explicitly mentioned. Each of the elements or features can beimplemented in a form failing to be combined with other elements orfeatures. Moreover, it is able to implement an embodiment of the presentinvention by combining elements and/or features together in part. Asequence of operations explained for each embodiment of the presentinvention can be modified. Some configurations or features of oneembodiment can be included in another embodiment or can be substitutedfor corresponding configurations or features of another embodiment. And,it is apparently understandable that an embodiment is configured bycombining claims failing to have relation of explicit citation in theappended claims together or can be included as new claims by amendmentafter filing an application.

In this disclosure, a specific operation explained as performed by aneNode B may be performed by an upper node of the eNode B in some cases.In particular, in a network constructed with a plurality of networknodes including an eNode B, it is apparent that various operationsperformed for communication with a user equipment can be performed by aneNode B or other networks except the eNode B. ‘eNode B (eNB)’ may besubstituted with such a terminology as a fixed station, a Node B, a basestation (BS), an access point (AP) and the like.

Embodiments of the present invention can be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof. In the implementation by hardware, a method according to eachembodiment of the present invention can be implemented by at least oneselected from the group consisting of ASICs (application specificintegrated circuits), DSPs (digital signal processors), DSPDs (digitalsignal processing devices), PLDs (programmable logic devices), FPGAs(field programmable gate arrays), processor, controller,microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in amemory unit and is then drivable by a processor. The memory unit isprovided within or outside the processor to exchange data with theprocessor through the various means known in public.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

Although a method of receiving a downlink data channel in amulticell-based wireless communication system and an apparatus thereforare described with reference to examples applied to 3GPP LTE system, itmay be applicable to various kinds of wireless communication systems aswell as the 3GPP LTE system.

What is claimed is:
 1. A method for receiving a user equipment (UE)specific reference signal based-downlink data channel at a UE in awireless communication system, the method comprising: receiving, by theUE, one or more configurations including information on a certainreference signal which is assumed to be quasi co-located with aUE-specific reference signal from a network via an upper layer;detecting, by the UE, scheduling information of the UE-specificreference signal based-downlink data channel from the network; andreceiving, by the UE, specific reference signal based-downlink datachannel from the network based on the scheduling information, whereinthe scheduling information comprises an indicator indicating one of theone or more configurations, and wherein a large scale property for theUE-specific reference signal is obtained based on the certain referencesignal which is assumed to be quasi co-located with the UE-specificreference signal.
 2. The method of claim 1, wherein the certainreference signal is a channel status information-reference signal(CSI-RS).
 3. The method of claim 1, wherein the information on thecertain reference signal indicates a resource configuration of thecertain reference signal.
 4. The method of claim 1, wherein the largescale property comprises at least one of Doppler spread, Doppler shift,average delay and delay spread.
 5. A method for transmitting a userequipment (UE)-specific reference signal based-downlink data channel ata base station in a wireless communication system, the methodcomprising: transmitting, by the base station, one or moreconfigurations including information on a certain reference signal whichis assumed to be quasi co-located with a UE-specific reference signal toa UE via an upper layer; transmitting, by the base station, schedulinginformation of the UE-specific reference signal based-downlink datachannel to the UE; and transmitting, by the base station, theUE-specific reference signal based-downlink data channel to the UE whichreceives the UE-specific reference signal based-downlink data channelfrom the base station based on the scheduling information, wherein thescheduling information comprises an indicator indicating one of the oneor more configurations, and wherein a large scale property for theUE-specific reference signal is obtained based on the certain referencesignal which is assumed to be quasi co-located with the UE-specificreference signal.
 6. The method of claim 5, wherein the certainreference signal is a channel status information-reference signal(CSI-RS).
 7. The method of claim 5, wherein the information on thecertain reference signal indicates a resource configuration of thecertain reference signal.
 8. The method of claim 5, wherein the largescale property comprises at least one of Doppler spread, Doppler shift,average delay and delay spread.